Simple rule parsing
Parsing of nested rules

Credit due to Nigel Thorne for his solution for parsing indented data
structures with parslet given via stackoverflow[1].

[1] http://stackoverflow.com/a/16563186/800501
Integrate rules parsing
Make test a little clearer
Move engine logic out of models

The engine will be separate and the models will be simple value objects.

Left the engine spec as pending for now.
tidy up
Tighten up nested rule parsing

only accept a nested rule statement if it has at least one inner rule
Improve wording of specs
Temporarily skip unimplemented scenario
Merge pull request #5 from alphagov/integrate-rules-parsing

Integrate rules parsing